One thing you need to be aware of, if you don't already know, is that modules written for 5.6.x that use XS code are not binary compatible with 5.8.x, which means they will need to be recompiled.

You really don't want to do that on an individual module basis. So, the best upgrade path is to wipe out 5.6.1 and do a clean install of 5.8.8 or preferably 5.10.1. Then install any additional modules that you require and test your scripts.

The actual perl upgrade is easiest portion of the process. If your scripts are coded in the typical 5.6 style, then upgrading them to the current coding standards will be a chore.

So, if I understand you correctly, you want to have both 5.6.1 and 5.8.8 in your dev environment so that you can test the scripts in each perl environment without having to change the prod system. Is that correct?

I've done a little searching and have not found any old binaries for download. Activestate does state that they have archives of these available, if you're willing to pay for their ($1,000) Business Edition.

That's not the approach I'd take, but it would be the easiest. I'd download the source code, which is available at the link I provided in my prior post, and compile it myself.